Roughly 20,000 students in 43 flooded and damaged schools from Lower Manhattan to the Rockaways will temporarily move into other buildings, sometimes miles away, so that they don’t miss any more days of class, officials said.

The city made 1.2 million robo-calls to inform families of the changes — and will also use dozens of extra buses to shuttle students from shuttered buildings to their new schools — but Schools Chancellor Dennis Walcott still predicted some confusion.

“Tomorrow’s not going to be easy,” Walcott said in a NY1 interview Tuesday evening. “These first couple of days back, especially for the dislocated schools, is going to be a tough challenge, especially with the nor’easter.”

In addition to the 43 relocated schools, 22 other schools serving about 13,000 students will not reopen on Wednesday. That includes 13 schools that do not yet have power and nine that are still serving as shelters for displaced hurricane victims. Many of those schools will reopen on Thursday.

Some of the relocated schools will provide busing for students — buses will leave at 7 a.m. from closed elementary and middle schools and 10 a.m. from closed high schools — while other schools will give MetroCards to students or reimburse parents for driving to the new schools.

Special education students will continue receiving door-to-door bus service to their new school, but Walcott warned that the process of working out new bus routes could be “dicey.”

“We ask for patience,” Walcott said.

Walcott also acknowledged that some of the school relocations are not ideal, including situations where elementary and high school students have to share buildings.

But Walcott said the space crunch would also yield some interesting experiments, as in one Staten Island school that planned to fill its library with several classes of second-graders, all learning together with their teachers.

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